Mask blank, phase shift mask, and method for manufacturing semiconductor device

ABSTRACT

A mask blank with a phase shift film and a light shielding film, laminated on a transparent substrate. The phase shift film transmits ArF exposure light at a transmittance (τ) 2%≥τ≤30% and generates a phase difference (Δϕ) of 150°≥Δϕ≤200°, and is formed from a material containing Si and not substantially containing Cr, and has a lower layer (L) and an upper layer (U) laminated from the transparent substrate side. A refractive index n for layer L is below the transparent substrate while n for layer U is higher, and the layer L has an extinction coefficient k higher than layer U. The light shielding film includes a layer in contact with the phase shift film that is formed from a material containing Cr, has a n lower than layer U, and has an extinction coefficient k higher than layer U.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2016/078483 filed Sep. 27, 2016, claiming priority based onJapanese Patent Application No. 2015-193314, filed Sep. 30, 2015, thecontents of all of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a mask blank and a phase shift maskmanufactured using the mask blank. The present invention also relates toa method for manufacturing a semiconductor device using the phase shiftmask.

BACKGROUND ART

Generally, in a manufacturing process of a semiconductor device,photolithography is used to form a fine pattern. Multiple substratescalled transfer masks are usually utilized in forming the fine pattern.In miniaturization of a semiconductor device pattern, it is necessary toshorten the wavelength of an exposure light source used in thephotolithography, in addition to miniaturization of a mask patternformed in the transfer mask. Shortening of wavelength has been advancingrecently from the use of KrF excimer lasers (wavelength: 248 nm) to ArFexcimer lasers (wavelength: 193 nm) as exposure light sources in themanufacture of semiconductor devices.

As for the types of the transfer mask, a half tone phase shift mask isknown in addition to a conventional binary mask having a light shieldingpattern made of a chromium-based material on a transparent substrate.Molybdenum silicide (MoSi)-based materials are widely used for a phaseshift film of the half tone phase shift mask. However, as disclosed inPatent Document 1, it has been discovered recently that a MoSi-basedfilm has low resistance to exposure light of an ArF excimer laser(so-called ArF light fastness). In Patent Document 1, the ArF lightfastness of the MoSi-based film is enhanced by subjecting the MoSi-basedfilm after formation of a pattern to a plasma treatment, a UVirradiation treatment, or a heat treatment to form a passivation film ona surface of the pattern of the MoSi-based film.

In the half tone phase shift mask, a light shielding band is oftenprovided in a peripheral portion around a transfer pattern formingregion where a phase shift pattern is formed. Even within the transferpattern forming region, a relatively large-size phase shift pattern mayhave a smaller light shielding pattern laminated thereon. PatentDocument 2 discloses a mask blank for manufacturing a half tone phaseshift mask, which has a thin film structure including, from thesubstrate side, a metal silicide-based transfer mask film (lightsemitransmissive film), a light shielding film formed from achromium-based compound, and a hard mask film formed from a siliconcompound.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent Application Publication 2010-217514

Patent Document 2: International Publication WO 2004/090635

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

As described in Patent Document 2, a half tone phase shift masktypically includes a structure in which a half tone phase shift film(hereinafter referred to simply as a phase shift film) having a transferpattern (phase shift pattern) formed therein and a light shielding filmhaving a light shielding pattern such as a light shielding band formedtherein are laminated in this order on a transparent substrate. Such aphase shift mask is manufactured using a mask blank having a structurein which a phase shift film and a light shielding film are laminated inthis order on a transparent substrate. When manufacturing a phase shiftmask using this mask blank, it is necessary to form different patternsin the phase shift film and the light shielding film. Thus, materialswith different dry etching characteristics should be used for the phaseshift film and the light shielding film, respectively.

The phase shift film needs to have a function to transmit ArF exposurelight at a predetermined transmittance, and a function to generate apredetermined phase difference between the ArF exposure lighttransmitted through the phase shift film and the ArF exposure lighttransmitted through the air for the same distance as a thickness of thephase shift film. A material containing silicon can be easily adjustedto have optical properties suitable for forming the phase shift filmhaving these functions. In particular, transition metal silicide-basedmaterials are widely used for a phase shift film. If the materialcontaining silicon is used for a phase shift film, a material containingchromium is often used as a material of a light shielding film. If thelight shielding film is a multilayer film, the material containingchromium may be used for a layer in contact with the phase shift film(this layer may be regarded as an etching stopper film, i.e., anotherfunctional film). This is because a thin film formed from the materialcontaining chromium and a thin film formed from the material containingsilicon have high etching selectivity with respect to one another duringthe patterning by dry etching.

When a phase shift mask is set on a mask stage of an exposure apparatusto exposure-transfer a transfer pattern to a transfer target object suchas a resist film on a semiconductor substrate, exposure light istypically irradiated from the transparent substrate side of the phaseshift mask. As for the phase shift mask which includes the phase shiftfilm formed from the material containing silicon and the light shieldingfilm formed from the material containing chromium (also including alight shielding film having a layer in contact with the phase shift filmthat is formed from the material containing chromium) as describedabove, it was newly found that a phenomenon that chromium atoms in thelight shielding film move into the material containing silicon whichforms the phase shift film, so-called chromium migration, occurs whenthe exposure transfer with the exposure apparatus is repeated, which isproblematic.

If a large-size pattern of a phase shift film is placed in a phase shiftmask, a smaller pattern of a light shielding film may be provided on thelarge-size pattern. In this case, occurrence of chromium migration has aparticularly significant influence. When the phase shift mask set on amask stage of an exposure apparatus is irradiated with ArF exposurelight, and chromium atoms in the light shielding film are excited tocause many chromium atoms to move into the pattern of the phase shiftfilm, the transmittance of the phase shift film is decreased. In a halftone phase shift film, decrease in transmittance leads to reduction inphase shift effect generated between exposure light transmitted througha phase shift pattern and exposure light transmitted through atransparent portion, which becomes problematic. The chromium atoms movedinto the phase shift film may deposit onto side walls of the pattern ofthe phase shift film and exert a bad influence on a pattern image of theexposure light transmitted through the phase shift mask. Further, thechromium atoms moved into the phase shift film may deposit on a surfaceof a transparent substrate that is the transparent portion, which maycause fogging in the transparent portion (decrease in transmittance ofthe transparent portion).

Thus, the present invention was made to solve the existing problems.That is, an object of the present invention is to provide a mask blankwhich includes a phase shift film and a light shielding film laminatedin this order on a transparent substrate, wherein the phase shift filmis formed from a material containing silicon and not substantiallycontaining chromium, and a layer of the light shielding film at least incontact with the phase shift film is formed from a material containingchromium, nevertheless, if a phase shift mask manufactured from thismask blank is used for exposure transfer with an exposure apparatus,occurrence of chromium migration is significantly suppressed. A furtherobject is to provide a phase shift mask manufactured using this maskblank. Yet another object of the present invention is to provide amethod for manufacturing a semiconductor device using such a phase shiftmask.

Means for Solving the Problems

In order to solve the above problems, the present invention includes thefollowing structures.

(Structure 1)

A mask blank having a structure in which a phase shift film and a lightshielding film are laminated in this order on a transparent substrate,

wherein the phase shift film has a function to transmit exposure lightof an ArF excimer laser at a transmittance of not less than 2% and notmore than 30%, and a function to generate a phase difference of not lessthan 150 degrees and not more than 200 degrees between the exposurelight transmitted through the phase shift film and the exposure lighttransmitted through air for the same distance as a thickness of thephase shift film,

wherein the phase shift film is formed from a material containingsilicon and not substantially containing chromium, and includes astructure in which a lower layer and an upper layer are laminated fromthe transparent substrate side,

wherein the lower layer has a refractive index n lower than thetransparent substrate at a wavelength of the exposure light,

wherein the upper layer has a refractive index n higher than thetransparent substrate at a wavelength of the exposure light,

wherein the lower layer has an extinction coefficient k higher than theupper layer at a wavelength of the exposure light,

wherein the light shielding film includes a layer in contact with thephase shift film, and

wherein the layer in contact with the phase shift film is formed from amaterial containing chromium, has a refractive index n lower than theupper layer at a wavelength of the exposure light, and has an extinctioncoefficient k higher than the upper layer at a wavelength of theexposure light.

(Structure 2)

The mask blank according to Structure 1, wherein the upper layer has athickness greater than the lower layer.

(Structure 3)

The mask blank according to Structure 1 or 2, wherein the lower layerhas a thickness of less than 10 nm.

(Structure 4)

The mask blank according to any one of Structures 1 to 3, wherein therefractive index n of the lower layer is 1.5 or less.

(Structure 5)

The mask blank according to any one of Structures 1 to 4, wherein therefractive index n of the upper layer is greater than 2.0.

(Structure 6)

The mask blank according to any one of Structures 1 to 5, wherein therefractive index n of the layer in contact with the phase shift film is2.0 or less.

(Structure 7)

The mask blank according to any one of Structures 1 to 6, wherein theextinction coefficient k of the lower layer is 2.0 or more.

(Structure 8)

The mask blank according to any one of Structures 1 to 7, wherein anextinction coefficient k of the upper layer is 0.8 or less.

(Structure 9)

The mask blank according to any one of Structures 1 to 8, wherein theextinction coefficient k of the layer in contact with the phase shiftfilm is 1.0 or more.

(Structure 10)

The mask blank according to any one of Structures 1 to 9, wherein thelower layer is formed in contact with a surface of the transparentsubstrate.

(Structure 11)

The mask blank according to any one of Structures 1 to 10, wherein theupper layer has in its surface layer a layer having an oxygen contenthigher than in the portion of the upper layer excluding the surfacelayer.

(Structure 12)

The mask blank according to any one of Structures 1 to 11, wherein aback-surface reflectance to the exposure light entering from thetransparent substrate side is 30% or more.

(Structure 13)

A phase shift mask having a structure in which a phase shift film havinga transfer pattern formed therein and a light shielding film having alight shielding pattern formed therein are laminated in this order on atransparent substrate,

wherein the phase shift film has a function to transmit exposure lightof an ArF excimer laser at a transmittance of not less than 2% and notmore than 30%, and a function to generate a phase difference of not lessthan 150 degrees and not more than 200 degrees between the exposurelight transmitted through the phase shift film and the exposure lighttransmitted through air for the same distance as a thickness of thephase shift film,

wherein the phase shift film is formed from a material containingsilicon and not substantially containing chromium, and includes astructure in which a lower layer and an upper layer are laminated fromthe transparent substrate side,

wherein the lower layer has a refractive index n lower than thetransparent substrate at a wavelength of the exposure light,

wherein the upper layer has a refractive index n higher than thetransparent substrate at a wavelength of the exposure light,

wherein the lower layer has an extinction coefficient k higher than theupper layer at a wavelength of the exposure light,

wherein the light shielding film includes a layer in contact with thephase shift film, and

wherein the layer in contact with the phase shift film is formed from amaterial containing chromium, has a refractive index n lower than theupper layer at a wavelength of the exposure light, and has an extinctioncoefficient k higher than the upper layer at a wavelength of theexposure light.

(Structure 14)

The phase shift mask according to Structure 13, wherein the upper layerhas a thickness greater than the lower layer.

(Structure 15)

The phase shift mask according to Structure 13 or 14, wherein the lowerlayer has a thickness of less than 10 nm.

(Structure 16)

The phase shift mask according to any one of Structures 13 to 15,wherein the refractive index n of the lower layer is 1.5 or less.

(Structure 17)

The phase shift mask according to any one of Structures 13 to 16,wherein the refractive index n of the upper layer is greater than 2.0.

(Structure 18)

The phase shift mask according to any one of Structures 13 to 17,wherein the refractive index n of the layer in contact with the phaseshift film is 2.0 or less.

(Structure 19)

The phase shift mask according to any one of Structures 13 to 18,wherein the extinction coefficient k of the lower layer is 2.0 or more.

(Structure 20)

The phase shift mask according to any one of Structures 13 to 19,wherein an extinction coefficient k of the upper layer is 0.8 or less.

(Structure 21)

The phase shift mask according to any one of Structures 13 to 20,wherein the extinction coefficient k of the layer in contact with thephase shift film is 1.0 or more.

(Structure 22)

The phase shift mask according to any one of Structures 13 to 21,wherein the lower layer is formed in contact with a surface of thetransparent substrate.

(Structure 23)

The phase shift mask according to any one of Structures 13 to 22,wherein the upper layer has in its surface layer a layer having anoxygen content higher than in the portion of the upper layer excludingthe surface layer.

(Structure 24)

The phase shift mask according to any one of Structures 13 to 23,wherein a back-surface reflectance to the exposure light entering fromthe transparent substrate side is 30% or more.

(Structure 25)

A method for manufacturing a semiconductor device including a step ofusing the phase shift mask according to any one of Structures 13 to 24and exposure-transferring a transfer pattern to a resist film on asemiconductor substrate.

Effect of the Invention

The mask blank according to the present invention includes a phase shiftfilm and a light shielding film laminated in this order on a transparentsubstrate, the phase shift film is formed from a material containingsilicon and not substantially containing chromium, and a layer of thelight shielding film at least in contact with the phase shift film isformed from a material containing chromium. Nevertheless, if a phaseshift mask manufactured from this mask blank is used for the exposuretransfer with an exposure apparatus, occurrence of chromium migration,which is a phenomenon that chromium atoms in the light shielding filmmove into the phase shift film, can be significantly suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a structure of a mask blankaccording to an embodiment of the present invention.

FIGS. 2(a) to 2(g) are schematic cross-sectional views showing amanufacturing process of a phase shift mask according to an embodimentof the present invention.

DESCRIPTION OF THE EMBODIMENTS

The embodiments of the present invention are explained below. Regardinga phase shift mask which includes a phase shift film formed from amaterial containing silicon and a light shielding film formed from amaterial containing chromium laminated on a transparent substrate, theinventors made diligent studies on a means of suppressing the occurrenceof a phenomenon that chromium atoms in the light shielding film moveinto the material containing silicon constituting the phase shift film,i.e., chromium migration. The inventors found that the chromiummigration occurs due to photoexcitation of silicon in the phase shiftfilm and chromium in the light shielding film by ArF exposure light.

While ArF exposure light entering an interior of the transparentsubstrate of the phase shift mask is partially reflected at an interfacebetween a main surface of the substrate and a pattern of the phase shiftfilm, the ArF exposure light largely enters an interior of the phaseshift film. The phase shift film needs to have a function to transmitthe ArF exposure light at a predetermined transmittance. Thus, the phaseshift film has an optical property of absorbing most of the ArF exposurelight entering the interior of the phase shift film. Respective atoms ofsilicon and transition metal constituting the phase shift film which hasabsorbed energy of the ArF exposure light are photoexcited by absorbingthe energy.

In a region of the phase shift mask where a pattern of the lightshielding film is laminated on a pattern of the phase shift film, whilethe ArF exposure light transmitted through the phase shift film ispartially reflected at an interface between the phase shift film and thelight shielding film, the remainder enters an interior of the lightshielding film. Then, most of the ArF exposure light is absorbed withinthe light shielding film, and an amount of ArF exposure light exitingfrom the light shielding film is very small (for example, attenuation tothe light amount of 0.01% relative to the amount of ArF exposure lightbefore entering the phase shift film). At this time, within the lightshielding film, chromium atoms absorb the energy of ArF exposure light,and are photoexcited.

When the chromium atoms in the light shielding film and constituentelements in the phase shift film are photoexcited, the chromium atomsphotoexcited within the light shielding film are prone to enter theinterior of the phase shift film. As described above, the design conceptof the conventional phase shift film is configured such that the ArFexposure light is absorbed within the phase shift film to control thetransmittance. The light shielding film also has a similar designconcept. With the design concept of the conventional phase shift filmand light shielding film, a ratio of atoms photoexcited upon irradiationof the ArF exposure light among all atoms constituting the films becomesinevitably high, and thus, it is difficult to suppress the occurrence ofchromium migration.

The inventors considered that the ratio of silicon atoms photoexcited bythe ArF exposure light among all the silicon atoms constituting thephase shift film may be decreased by increasing a reflectance(back-surface reflectance) at an interface between the transparentsubstrate and the phase shift film compared to conventional phase shiftfilms so as to achieve a predetermined transmittance value of the phaseshift film to the ArF exposure light. When the ArF exposure light entersthe phase shift film from the transparent substrate side, an amount ofexposure light entering the interior of the phase shift film can bereduced by increasing the amount of ArF exposure light reflected at theinterface between the transparent substrate and the phase shift film bymore than what has been conventionally done. This allows the amount ofArF exposure light exiting from the phase shift film to be equivalent tothat of the conventional phase shift film, even if the amount of ArFexposure light absorbed in the phase shift film is reduced by more thanwhat has been conventionally done. As a result, the inventors found thatthe silicon atoms are less likely to be photoexcited within the phaseshift film, so that movement of photoexcited chromium atoms from thelight shielding film into the phase shift film can be suppressed.

Additionally, the inventors considered that the ratio of chromium atomsphotoexcited by the ArF exposure light among all the chromium atomsconstituting the light shielding film may be decreased by increasing areflectance (back-surface reflectance) at the interface between thephase shift film and the light shielding film compared to theconventional case so as to ensure light shielding performance of thelight shielding film for the ArF exposure light. The amount of exposurelight entering an interior of the light shielding film can be reduced byincreasing the amount of ArF exposure light reflected at the interfacebetween the phase shift film and the light shielding film by more thanwhat has been conventionally done. This allows for the light shieldingfilm to have the light shielding performance equivalent to theconventional light shielding film, even if the amount of ArF exposurelight absorbed in the light shielding film is reduced by more than whathas been conventionally done. As a result, the inventors found that thechromium atoms are less likely to be photoexcited within the lightshielding film, so that movement of the chromium atoms into the phaseshift film can be suppressed.

Then, the inventors first examined the increase of reflectance at theinterface between the phase shift film and the transparent substratesuch that it becomes higher than in the conventional phase shift film.In order to increase the back-surface reflectance of the phase shiftfilm provided on the transparent substrate, a layer of the phase shiftfilm at least in contact with the transparent substrate should be formedfrom a material having a high extinction coefficient k at a wavelengthof ArF exposure light (the extinction coefficient k at a wavelength ofArF exposure light is hereinafter referred to simply as an extinctioncoefficient k). The phase shift film of a single layer structure istypically formed from a material which has a high refractive index n ata wavelength of ArF exposure light (the refractive index n at awavelength of ArF exposure light is hereinafter referred to simply as arefractive index n) and a low extinction coefficient k, since it isnecessary to satisfy the required optical properties and thickness.Then, the inventors examined the increase of back-surface reflectance ofthe phase shift film by adjusting composition of a material forming thephase shift film to significantly increase the extinction coefficient k.Since this adjustment causes the phase shift film to fail to satisfy theconditions of transmittance within a predetermined range, it becomesnecessary to significantly reduce the thickness of the phase shift film.However, if the thickness of the phase shift film is reduced, the phaseshift film cannot satisfy the conditions of phase difference within apredetermined range. Since there is a limit to the increase ofrefractive index n of the material forming the phase shift film, it isdifficult to increase the back-surface reflectance in a single-layerphase shift film.

Then, based on the design concept that the phase shift film is alaminated structure including a lower layer and an upper layer and theback-surface reflectance is increased in the entire laminated structure,the inventors made a further study. For the upper layer of the phaseshift film on the side away from the transparent substrate, they decidedto apply a material having a high refractive index n and a lowextinction coefficient k, as in the conventional single-layer phaseshift film. On the other hand, for the lower layer of the phase shiftfilm located on the transparent substrate side, they decided to apply amaterial having a higher extinction coefficient k than the material ofthe conventional phase shift film. Since such a lower layer functions todecrease the transmittance of the phase shift film, it becomes necessaryto reduce the thickness of the lower layer. When the thickness of thelower layer is reduced, an amount of exposure light transmitted throughthe lower layer increases, and thus, the back-surface reflectance isdecreased. Consequently, the inventors decided to make the refractiveindex n of the lower layer less than that of the transparent substratein order to further increase the back-surface reflectance. The inventorsfound that this makes a large difference in refractive index n betweenthe lower layer and the upper layer, and increases an amount of exposurelight reflected at an interface between the lower layer and the upperlayer, and thus the back-surface reflectance of the phase shift film canbe increased.

Next, the inventors examined the increase of reflectance to the ArFexposure light at the interface between the phase shift film and thelight shielding film. A common method for increasing the reflectance isto form a layer of the light shielding film in contact with the upperlayer of the phase shift film from a material having a refractive indexn higher than the upper layer of the phase shift film. The materialhaving a refractive index n higher than the upper layer of the phaseshift film should have a high nitrogen content. However, since thematerial having a high nitrogen content tends to have a low extinctioncoefficient k, it is not favorable to a layer forming the lightshielding film. In view of this matter, the inventors decided to formthe layer of the light shielding film in contact with the upper layer ofthe phase shift film from a material that has a high extinctioncoefficient k and a low refractive index n relative to the phase shiftfilm. In this way, even a light shielding film with a small thicknesscan ensure sufficient light shielding performance while achieving a highreflectance to the ArF exposure light at an interface between the upperlayer of the phase shift film and the light shielding film. It wasconcluded that the above technical problems can be solved by thestructure of the phase shift film and the light shielding film as statedabove.

That is, the present invention is a mask blank having a structure inwhich a phase shift film and a light shielding film are laminated inthis order on a transparent substrate, and further including thefollowing features. The phase shift film has a function to transmitexposure light of an ArF excimer laser at a transmittance of not lessthan 2% and not more than 30%, and a function to generate a phasedifference of not less than 150 degrees and not more than 200 degrees(more preferably, not less than 150 degrees and not more than 180degrees) between the exposure light transmitted through the phase shiftfilm and the exposure light transmitted through air for the samedistance as a thickness of the phase shift film. Additionally, the phaseshift film is formed from a material containing silicon and notsubstantially containing chromium, and includes a structure in which alower layer and an upper layer are laminated from the transparentsubstrate side. The lower layer of the phase shift film has a refractiveindex n lower than the transparent substrate at a wavelength of theexposure light. The upper layer of the phase shift film has a refractiveindex n higher than the transparent substrate at a wavelength of theexposure light. The lower layer of the phase shift film has anextinction coefficient k higher than the upper layer at a wavelength ofthe exposure light. The light shielding film includes a layer in contactwith the phase shift film. The layer in contact with the phase shiftfilm is formed from a material containing chromium, has a refractiveindex n lower than the upper layer at a wavelength of the exposurelight, and has an extinction coefficient k higher than the upper layerat a wavelength of the exposure light.

FIG. 1 is a cross-sectional view showing a structure of a mask blank 100according to an embodiment of the present invention. The mask blank 100of the present invention shown in FIG. 1 has a structure in which aphase shift film 2, a light shielding film 3, and a hard mask film 4 arelaminated in this order on a transparent substrate 1.

The transparent substrate 1 can be formed from quartz glass,aluminosilicate glass, soda-lime glass, low thermal expansion glass(such as SiO₂—TiO₂ glass), etc. as well as synthetic quartz glass. Amongthe above, the synthetic quartz glass is particularly preferable as amaterial forming the transparent substrate 1 of the mask blank 100 sinceit has a high transmittance to ArF excimer laser light. A refractiveindex n of the material forming the transparent substrate 1 at awavelength of ArF exposure light (about 193 nm) is preferably not lessthan 1.50 and not more than 1.60, more preferably not less than 1.52 andnot more than 1.59, and even more preferably not less than 1.54 and notmore than 1.58.

The phase shift film 2 is required to have a transmittance of 2% or moreto the Arf exposure light. In order to generate a sufficient phase shifteffect between the exposure light transmitted through the phase shiftfilm 2 and the exposure light transmitted through the air, thetransmittance to the exposure light should be at least 2%. Thetransmittance of the phase shift film 2 to the exposure light ispreferably 3% or more, and more preferably 4% or more. However, as thetransmittance of the phase shift film 2 to the exposure light increases,it will be more difficult to increase the back-surface reflectance.Thus, the transmittance of the phase shift film 2 to the exposure lightis preferably 30% or less, more preferably 20% or less, and even morepreferably 10% or less.

In order to obtain a proper phase shift effect, it is desired for thephase shift film 2 to be adjusted such that the phase differencegenerated between the ArF exposure light transmitted through the phaseshift film 2 and the light transmitted through the air for the samedistance as a thickness of the phase shift film 2 is within the range ofnot less than 150 degrees and not more than 200 degrees. The phasedifference of the phase shift film 2 is preferably 155 degrees or more,and more preferably 160 degrees or more. Also, the phase difference ofthe phase shift film 2 is preferably 190 degrees or less, morepreferably 180 degrees or less, and even more preferably 179 degrees orless. This is because it is possible to reduce an influence of increasein phase difference caused by microscopic etching of the transparentsubstrate 1 upon dry etching in forming a pattern in the phase shiftfilm 2. This is also because recent methods for irradiating a phaseshift mask with ArF exposure light by an exposure apparatus often makethe ArF exposure light incident from a direction that is oblique at apredetermined angle to a vertical direction of a surface of the phaseshift film 2.

The mask blank 100 preferably has a reflectance (back-surfacereflectance) of 30% or more when the ArF exposure light is irradiatedfrom the transparent substrate 1 side while the phase shift film 2 andthe light shielding film 3 are laminated on the transparent substrate 1.The back-surface reflectance of 30% or more can suppress photoexcitationof silicon atoms in the phase shift film 2 and chromium atoms in thelight shielding film 3. This suppressive effect can suppress chromiummigration, which is a phenomenon that the chromium atoms in the lightshielding film 3 move into the phase shift film 2. On the other hand, ifthe back-surface reflectance is too high, when the exposure transfer toa transfer target object (such as a resist film on a semiconductorwafer) is conducted using the phase shift mask manufactured from thismask blank 100, an exposure transfer image will be profoundly affectedby reflected light on the back surface side of the phase shift mask,which is not preferable. From this viewpoint, the back-surfacereflectance is preferably 45% or less, and more preferably 40% or less.

The phase shift film 2 has a structure in which a lower layer 21 and anupper layer 22 are laminated from the transparent substrate 1 side. Itis necessary that the entire phase shift film 2 satisfies the aboveconditions of transmittance and phase difference and the back-surfacereflectance in the laminated structure of the phase shift film 2 and thelight shielding film 3 satisfies the above described conditions. Inorder to satisfy these conditions, the refractive index n of the lowerlayer 21 of the phase shift film 2 should be at least lower than that ofthe transparent substrate 1. At the same time, the refractive index n ofthe upper layer 22 should be at least higher than that of thetransparent substrate 1. Additionally, the extinction coefficient k ofthe lower layer 21 should be at least higher than that of the upperlayer 22. Incidentally, the upper layer 22 is preferably thicker thanthe lower layer 21.

In order to satisfy the above described relation between the lower layer21 and the upper layer 22 of the phase shift film 2, the refractiveindex n of the lower layer 21 should be 1.50 or less. The refractiveindex n of the lower layer 21 is preferably 1.45 or less, and morepreferably 1.40 or less. Further, the refractive index n of the lowerlayer 21 is preferably 1.00 or more, and more preferably 1.10 or more.The extinction coefficient k of the lower layer 21 should be 2.00 ormore. The extinction coefficient k of the lower layer 21 is preferably2.20 or more, and more preferably 2.40 or more. Further, the extinctioncoefficient k of the lower layer 21 is preferably 3.30 or less, and morepreferably 3.10 or less. The refractive index n and extinctioncoefficient k of the lower layer 21 are values derived by regarding theentire lower layer 21 as a single, optically uniform layer.

Also, in order to satisfy the above described relation between the lowerlayer 21 and the upper layer 22 of the phase shift film 2, therefractive index n of the upper layer 22 should be greater than 2.00.The refractive index n of the upper layer 22 is preferably 2.10 or more.Further, the refractive index n of the upper layer 22 is preferably 3.00or less, and more preferably 2.80 or less. The extinction coefficient kof the upper layer 22 should be 0.80 or less. The extinction coefficientk of the upper layer 22 is preferably 0.60 or less, and more preferably0.50 or less. Further, the extinction coefficient k of the upper layer22 is preferably 0.10 or more, and more preferably 0.20 or more. Therefractive index n and extinction coefficient k of the upper layer 22are values derived by regarding the entire upper layer 22 including asurface layer portion described below as a single, optically uniformlayer.

The refractive index n and extinction coefficient k of a thin filmincluding the phase shift film 2 are not determined only by thecomposition of the thin film. Film density and crystal condition of thethin film are also factors that affect the refractive index n andextinction coefficient k. Thus, the conditions in forming a thin film byreactive sputtering are adjusted so that the thin film reaches desiredrefractive index n and extinction coefficient k. The condition formaking the lower layer 21 and the upper layer 22 within the range ofrefractive index n and extinction coefficient k mentioned above is notlimited to adjustment of the ratio of a noble gas and a reactive gas(such as an oxygen gas or a nitrogen gas) in a mixed gas in forming thefilm by reactive sputtering, but includes various conditions such aspressure in a film forming chamber, power applied to a sputteringtarget, positional relationship between the target and the transparentsubstrate 1 such as distance, etc. in film formation through reactivesputtering. Further, these film forming conditions are specific to afilm forming apparatus, and are adjusted arbitrarily so that the lowerlayer 21 and the upper layer 22 to be formed achieve the desiredrefractive index n and extinction coefficient k.

The thickness of the entire phase shift film 2 is desirably less than100 nm. In a mask blank for manufacturing a phase shift mask, biasrelated to Electro Magnetic Field (EMF) effect is desirably small. Thisis because reduction in thickness of a thin film pattern of the phaseshift mask is effective to decrease the EMF bias. However, it is alsonecessary to satisfy the above described relation of thickness betweenthe lower layer 21 and the upper layer 22 of the phase shift film 2.Particularly considering the transmittance of the entire phase shiftfilm 2 to the ArF exposure light, the thickness of the lower layer 21 ispreferably less than 10 nm, more preferably 9 nm or less, and even morepreferably 8 nm or less. Further, particularly considering theback-surface reflectance of the phase shift film 2, the thickness of thelower layer 21 is preferably 3 nm or more, more preferably 4 nm or more,and even more preferably 5 nm or more.

Particularly considering the phase difference and back-surfacereflectance of the entire phase shift film 2 to the ArF exposure light,the thickness of the upper layer 22 is preferably 9 times or more thethickness of the lower layer 21, and more preferably 10 times or more.Further, particularly considering that the phase shift film 2 isprepared to have a thickness of less than 100 nm, the thickness of theupper layer 22 is preferably 15 times or less the thickness of the lowerlayer 21, and more preferably 13 times or less. Also, the thickness ofthe upper layer 22 is preferably 90 nm or less, and more preferably 80nm or less.

Both the lower layer 21 and the upper layer 22 of the phase shift film 2are formed from a material containing silicon and not substantiallycontaining chromium. It is preferable that the phase shift film 2further contains metallic elements other than chromium. The metallicelements to be contained in the material forming the phase shift film 2are preferably transition metal elements. The transition metal elementsin this case include one or more metallic elements of molybdenum (Mo),tantalum (Ta), tungsten (W), titanium (Ti), hafnium (Hf), nickel (Ni),vanadium (V), zirconium (Zr), ruthenium (Ru), rhodium (Rh), zinc (Zn),niobium (Nb), and palladium (Pd). The metallic elements other than thetransition metal elements to be contained in the material forming thephase shift film 2 include, for example, aluminum (Al), indium (In), tin(Sn), and gallium (Ga). In addition to the elements above, the materialforming the phase shift film 2 may contain elements such as carbon (C),hydrogen (H), boron (B), germanium (Ge), and antimony (Sb). Further, thematerial forming the lower layer 21 may contain an inert gas such ashelium (He), argon (Ar), krypton (Kr), and xenon (Xe).

The lower layer 21 of the phase shift film 2 is preferably formed from amaterial which contains metal other than chromium and silicon and whichdoes not substantially contain chromium and oxygen. This is because,while a material having a high extinction coefficient k should be usedfor the lower layer 21, the increase of oxygen content in the materialcauses the extinction coefficient k to be significantly lowered, whichis undesirable. Thus, the lower layer 21 should be formed from amaterial not substantially containing oxygen. The material notsubstantially containing oxygen is a material having the oxygen contentof at least 5 atomic % or less. The oxygen content in the materialforming the lower layer 21 is preferably 3 atomic % or less, and morepreferably not more than the detection lower limit upon compositionanalysis through, for example, X-ray photoelectron spectroscopy.

The material forming the lower layer 21 may also contain nitrogen.However, as the nitrogen content in the material increases, therefractive index n of the material tends to increase. Further, as thenitrogen content in the material increases, the extinction coefficient kof the material tends to decrease, though not to the extent of decreasedue to increase in oxygen content. The material forming the lower layer21 preferably has a low refractive index n and a high extinctioncoefficient k. In view of these points, when the lower layer 21 isformed from a material including metal, silicon, and nitrogen, thenitrogen content is preferably 20 atomic % or less, more preferably 19atomic % or less, and even more preferably 15 atomic % or less. In thiscase, however, the nitrogen content in the material forming the lowerlayer 21 is preferably 5 atomic % or more, and more preferably 10 atomic% or more. The lower layer 21 is more preferably formed from a materialincluding metal other than chromium and silicon, or a material includingmetal other than chromium, silicon, and nitrogen, and even morepreferably formed from the material including metal other than chromiumand silicon.

The lower layer 21 is preferably formed in contact with a surface of thetransparent substrate 1. This is because a structure in which the lowerlayer 21 contacts the surface of the transparent substrate 1 can improvethe effect of enhancing the back-surface reflectance that is generatedby the laminated structure of the phase shift film 2 including the lowerlayer 21 and the upper layer 22 as stated above. An etching stopper filmmay be provided between the transparent substrate 1 and the phase shiftfilm 2 as long as it has less influence on the effect of enhancing theback-surface reflectance of the phase shift film 2. In this case, thethickness of the etching stopper film needs to be 10 nm or less,preferably 7 nm or less, and more preferably 5 nm or less. From theviewpoint of an effective function as an etching stopper, the thicknessof the etching stopper film needs to be 3 nm or more. An extinctioncoefficient k of a material forming the etching stopper film should beless than 0.1, preferably 0.05 or less, and more preferably 0.01 orless. Further, a refractive index n of the material forming the etchingstopper film in this case should at least be 1.9 or less, and preferably1.7 or less. The refractive index n of the material forming the etchingstopper film is preferably 1.55 or more.

The upper layer 22 of the phase shift film 2 is preferably formed from amaterial which contains metal other than chromium, silicon, nitrogen,and oxygen and which does not substantially contain chromium. Since thelower layer 21 of the phase shift film 2 should be formed from amaterial with a high extinction coefficient k, the upper layer 22 shouldcontain not only nitrogen but also oxygen in a positive manner. In viewof this point, the oxygen content in the material forming the upperlayer 22 is preferably higher than 5 atomic %, more preferably 10 atomic% or more, and even more preferably 12 atomic % or more. Oxygen tends todecrease both the refractive index n and extinction coefficient k of amaterial as the oxygen content in the material increases. Thus, theincrease in oxygen content in the upper layer 22 leads to the increasein entire thickness of the phase shift film 2 to be required to ensurethe predetermined transmittance and phase difference of the entire phaseshift film 2 to the ArF exposure light. In view of these points, theoxygen content in the material forming the upper layer 22 is preferably30 atomic % or less, more preferably 25 atomic % or less, and even morepreferably 20 atomic % or less.

Nitrogen tends to increase the refractive index n and decrease theextinction coefficient k of a material as the nitrogen content in thematerial increases. The nitrogen content in the material forming theupper layer 22 is preferably 20 atomic % or more, more preferably 25atomic % or more, and even more preferably 30 atomic % or more. Further,the nitrogen content in the material forming the upper layer 22 ispreferably 50 atomic % or less, more preferably 45 atomic % or less, andeven more preferably 40 atomic % or less.

A ratio [%] of the metal content [atomic %] divided by the total contentof metal and silicon [atomic %] in the material forming the upper layer22 (hereinafter referred to as “M/[M+Si] ratio”) should be lower thanthe M/[M+Si] ratio of the lower layer 21. When a material has theM/[M+Si] ratio within a range from 0 to about 34%, both the refractiveindex n and extinction coefficient k tend to increase as the M/[M+Si]ratio increases. A material used for the upper layer 22 should have atendency to have a high refractive index n and a low extinctioncoefficient k, and preferably has a low M/[M+Si] ratio. On the otherhand, a material used for the lower layer 21 should have a tendency tohave a low refractive index n and a high extinction coefficient k, andpreferably has a certain high level of M/[M+Si] ratio.

A difference obtained by subtracting the M/[M+Si] ratio in the upperlayer 22 from the M/[M+Si] ratio in the lower layer 21 is preferably atleast 1% or more. Further, the difference obtained by subtracting theM/[M+Si] ratio in the upper layer 22 from the M/[M+Si] ratio in thelower layer 21 is preferably at least 10% or less, and more preferably8% or less. The M/[M+Si] ratio in the material forming the lower layer21 should be at least 8% or more, preferably 9% or more, and morepreferably 10% or more. Further, the M/[M+Si] ratio in the materialforming the lower layer 21 should be at least 20% or less, preferably15% or less, and more preferably 12% or less.

From the viewpoint of reduction in variation of transmittance and phaseshift amount of the phase shift film 2, it is desirable not only tocontain oxygen in the upper layer 22 in advance but also to decrease themetal content in the upper layer 22. However, if the material formingthe upper layer 22 of the phase shift film 2 does not contain metallicelements which contribute to the increase in refractive index n andextinction coefficient k, the problem of thickening of the entire phaseshift film 2 arises. When the upper layer 22 is formed by a DCsputtering method, there is also a problem of increase in defects due tolow conductivity of a metal silicide target. In view of these points,the M/[M+Si] ratio in the upper layer 22 is preferably 2% or more, andmore preferably 3% or more. Still, from the viewpoint of reduction invariation of transmittance and phase shift amount of the phase shiftfilm 2 (upper layer 22), the M/[M+Si] ratio in the upper layer 22 ispreferably 9% or less, and more preferably 8% or less.

Both the material forming the lower layer 21 and the material formingthe upper layer 22 preferably contain the same metallic elements. Theupper layer 22 and the lower layer 21 are patterned by dry etching usingthe same etching gas. Thus, the upper layer 22 and the lower layer 21are desirably etched in the same etching chamber. If respectivematerials forming the upper layer 22 and the lower layer 21 contain thesame metallic elements, environmental change in the etching chamber canbe reduced when the object to be dry-etched changes from the upper layer22 to the lower layer 21.

While the lower layer 21 and the upper layer 22 of the phase shift film2 are formed through sputtering, any sputtering such as DC sputtering,RF sputtering, and ion beam sputtering is applicable. Application of DCsputtering is preferable, considering the film forming rate. In the casewhere the target has low conductivity, while application of RFsputtering or ion beam sputtering is preferable, application of RFsputtering is more preferable considering the film forming rate.

In the steps of forming the lower layer 21 and the upper layer 22 ofphase shift film 2, respectively, through sputtering, it is impossibleto form the lower layer 21 and the upper layer 22 by the same singletarget. This is because the respective M/[M+Si] ratios in the lowerlayer 21 and the upper layer 22 are different from each other. If thelower layer 21 and the upper layer 22 are respectively formed from twotargets having different M/[M+Si] ratios, they may be formed in the samefilm forming chamber or in different film forming chambers. Also, thelower layer 21 and the upper layer 22 having different M/[M+Si] ratiosmay be formed by the sputtering using a silicon target and a metalsilicide target with varying voltage applied to respective targets. Ifthe lower layer 21 and the upper layer 22 are formed in different filmforming chambers, these film forming chambers are preferablycommunicated with each other, for example, via another vacuum chambertherebetween. In this case, the vacuum chamber is preferably coupled toa load lock chamber through which the transparent substrate 1 will passwhen introducing the transparent substrate 1 in the atmosphere into thevacuum chamber. Further, it is preferable to provide a transport device(robotic hand) for transporting the transparent substrate 1 between theload lock chamber, vacuum chamber, and respective film forming chambers.

The upper layer 22 desirably has in its surface layer a layer having anoxygen content higher than the portion of the upper layer 22 excludingthe surface layer (this layer is hereafter simply referred to as asurface oxidized layer). Various oxidation treatments are applicable asa method of forming the surface oxidized layer of the upper layer 22.The oxidation treatments include, for example, a heat treatment in a gascontaining oxygen such as the atmosphere, a light irradiation treatmentusing a flash lamp, etc. in a gas containing oxygen, and a treatment tobring ozone and oxygen plasma into contact with the surface layer of theupper layer 22. It is particularly preferable to form the surfaceoxidized layer in the upper layer 22 using the heat treatment or lightirradiation treatment using a flash lamp, etc. where an effect to reducefilm stress of the phase shift film 2 can be obtained simultaneously.The thickness of the surface oxidized layer of the upper layer 22 ispreferably 1 nm or more, and more preferably 1.5 nm or more. Further,the thickness of the surface oxidized layer of the upper layer 22 ispreferably 5 nm or less, and more preferably 3 nm or less. Therefractive index n and extinction coefficient k of the upper layer 22described above are mean values for the entire upper layer 22 includingthe surface oxidized layer. Since a ratio of the surface oxidized layerin the upper layer 22 is considerably low, the existence of the surfaceoxidized layer has less influence on the refractive index n andextinction coefficient k of the entire upper layer 22.

The lower layer 21 may be formed from a material including silicon, or amaterial including silicon and one or more elements selected fromnonmetallic elements other than oxygen and metalloid elements. The lowerlayer 21 may contain any metalloid elements in addition to silicon.Among these metalloid elements, it is preferable to contain one or moreelements selected from boron, germanium, antimony, and tellurium, sinceenhancement in conductivity of silicon to be used as a sputtering targetcan be expected.

The lower layer 21 may contain nonmetallic elements other than oxygen.Among these nonmetallic elements, it is preferable to contain one ormore elements selected from nitrogen, carbon, fluorine, and hydrogen.These nonmetallic elements include a noble gas such as helium (He),argon (Ar), krypton (Kr), and xenon (Xe). Oxygen is not contained in thelower layer 21 in a positive manner (when composition analysis is madethrough, for example, X-ray photoelectron spectroscopy, the oxygencontent is preferably not more than the detection lower limit). This isfor the purpose of preventing significant reduction of back-surfacereflectance of the phase shift film 2, since reduction of extinctioncoefficient k of the lower layer 21 caused by containing oxygen in thematerial forming the lower layer 21 is greater compared to othernonmetallic elements.

The lower layer 21 is preferably formed from a material includingsilicon and nitrogen, or a material containing silicon, nitrogen, andone or more elements selected from nonmetallic elements other thanoxygen and metalloid elements. This is because a silicon-based materialcontaining nitrogen has higher light fastness to the ArF exposure lightthan a silicon-based material free of nitrogen. Another reason is thatoxidation of pattern side walls is suppressed when a phase shift patternis formed in the lower layer 21. However, as the nitrogen content in thematerial forming the lower layer 21 increases, the refractive index nbecomes higher and the extinction coefficient k becomes lower.Therefore, the nitrogen content in the material forming the lower layer21 is preferably 40 atomic % or less, more preferably 36 atomic % orless, and even more preferably 32 atomic % or less.

The upper layer 22, excluding its surface layer portion, is formed froma material including silicon and nitrogen, or a material containingsilicon, nitrogen, and one or more elements selected from nonmetallicelements other than oxygen and metalloid elements. The surface layerportion of the upper layer 22 is located on the side opposite to thelower layer 21 side. After forming the phase shift film 2 on thetransparent substrate 1 with a film-forming apparatus, the film surfaceis subjected to a cleaning treatment. Since the surface layer portion ofthe upper layer 22 is exposed to cleaning liquid and rinsing liquidduring the cleaning treatment, progress of oxidation is inevitableregardless of composition upon film formation. Further, oxidation of thesurface layer portion of the upper layer 22 also progresses by exposureof the phase shift film 2 to the atmosphere and subjecting the phaseshift film 2 to a heat treatment in the atmosphere. As stated above, itis more preferable for the material of the upper layer 22 to have ahigher refractive index n. Since the refractive index n tends todecrease as the oxygen content in the material increases, oxygen is notcontained in the upper layer 22, excluding the surface layer portion, ina positive manner upon film formation (when composition analysis is madethrough, for example, X-ray photoelectron spectroscopy, the oxygencontent is preferably not more than the detection lower limit). Thus,the surface layer portion of the upper layer 22 will be formed from thematerial forming the upper layer 22 excluding the surface layer portionwith the addition of oxygen. The surface layer portion of the upperlayer 22 may be formed through various oxidation treatments statedabove.

The upper layer 22 may contain any metalloid elements in addition tosilicon. Among these metalloid elements, it is preferable to contain oneor more elements selected from boron, germanium, antimony, andtellurium, since enhancement in conductivity of silicon to be used as asputtering target can be expected.

The upper layer 22 may contain nonmetallic elements other than oxygen.Among these nonmetallic elements, it is preferable to contain one ormore elements selected from nitrogen, carbon, fluorine, and hydrogen.These nonmetallic elements include a noble gas such as helium (He),argon (Ar), krypton (Kr), and xenon (Xe). It is more preferable for thematerial of the upper layer 22 to have a higher refractive index n, andthe refractive index n of a silicon-based material tends to increase asthe nitrogen content increases. Therefore, the total content ofmetalloid and nonmetallic elements contained in the material forming theupper layer 22 is preferably 10 atomic % or less, and more preferably 5atomic % or less, and it is even more preferable for the material not tocontain such elements in a positive manner. On the other hand, for theabove reason, it is desired for the nitrogen content in the materialforming the upper layer 22 to be at least higher than the nitrogencontent in the material forming the lower layer 21. The nitrogen contentin the material forming the upper layer 22 is preferably higher than 50atomic %, more preferably 52 atomic % or more, and even more preferably55 atomic % or more.

Both the material forming the lower layer 21 and the material formingthe upper layer 22 excluding the surface layer portion are preferablycomprised of the same elements. The upper layer 22 and the lower layer21 are patterned by dry etching using the same etching gas. Thus, theupper layer 22 and the lower layer 21 are desirably etched in the sameetching chamber. If the respective materials forming the upper layer 22and the lower layer 21 are comprised of the same elements, environmentalchange in the etching chamber can be reduced when the object to bedry-etched changes from the upper layer 22 to the lower layer 21. Aratio of the etching rate of the lower layer 21 to the etching rate ofthe upper layer 22 when the phase shift film 2 is patterned by dryetching with the same etching gas is preferably 3.0 or less, and morepreferably 2.5 or less. Further, the ratio of the etching rate of thelower layer 21 to the etching rate of the upper layer 22 when the phaseshift film 2 is patterned by dry etching with the same etching gas ispreferably 1.0 or more.

The mask blank 100 has a light shielding film 3 on the phase shift film2. Generally, in a binary transfer mask, an outer peripheral regionoutside a region where a transfer pattern is formed (transfer patternforming region) is desired to ensure optical density (OD) of not lessthan a predetermined value so as to prevent a resist film on asemiconductor wafer from being subjected to an influence of exposurelight transmitted through the outer peripheral region when exposuretransfer is made on the resist film using an exposure apparatus. Thispoint is similar in the case of a phase shift mask. Generally, the outerperipheral region of a transfer mask including a phase shift maskpreferably has OD of 2.8 or more, and more preferably 3.0 or more. Thephase shift film 2 has a function to transmit the exposure light at apredetermined transmittance, and it is difficult to ensure the opticaldensity of a predetermined value with the phase shift film 2 alone.Therefore, it is necessary to laminate the light shielding film 3 on thephase shift film 2 at the stage of manufacturing the mask blank 100 inorder to ensure lacking optical density. With such a structure of themask blank 100, a phase shift mask 200 (see FIG. 2) ensuring the opticaldensity of the predetermined value in the outer peripheral region can bemanufactured by removing the light shielding film 3 in the region wherethe phase shift effect is used (basically transfer pattern formingregion) during manufacture of the phase shift mask 200.

The light shielding film 3 includes a layer at least in contact with thephase shift film 2 (upper layer 22). If the light shielding film 3 is asingle layer structure, the single-layer light shielding film 3 itselfis the layer in contact with the phase shift film 2 (upper layer 22). Ifthe light shielding film 3 is a laminated structure comprised of two ormore layers, its lowermost layer is the layer in contact with the phaseshift film 2 (upper layer 22). A material having sufficient etchingselectivity to an etching gas used in forming a pattern in the phaseshift film 2 should be used for the layer of the light shielding film 3in contact with the phase shift film 2. Thus, the layer of the lightshielding film 3 in contact with the phase shift film 2 is formed from amaterial containing chromium. The material containing chromium whichforms the layer of the light shielding film 3 in contact with the phaseshift film 2 can include, in addition to chromium metal, a materialcontaining chromium and one or more elements selected from oxygen,nitrogen, carbon, boron, and fluorine.

While a chromium-based material is generally etched by a mixed gas of achlorine-based gas and an oxygen gas, the etching rate of the chromiummetal to the etching gas is not so high. Considering the enhancement ofetching rate to the etching gas that is the mixed gas of thechlorine-based gas and oxygen gas, the material forming the lightshielding film 3 preferably contains chromium and one or more elementsselected from oxygen, nitrogen, carbon, boron, and fluorine. Further,the material containing chromium which forms the light shielding film 3may contain one or more elements among molybdenum, indium, and tin.Containing one or more elements among molybdenum, indium, and tin canincrease the etching rate to the mixed gas of the chlorine-based gas andoxygen gas.

The layer of the light shielding film 3 in contact with the phase shiftfilm 2 needs to have a refractive index n lower than the upper layer 22of the phase shift film 2. The refractive index n of the layer of thelight shielding film 3 in contact with the phase shift film 2 ispreferably 2.00 or less, more preferably less than 2.00, and even morepreferably 1.95 or less. Furthermore, the layer of the light shieldingfilm 3 in contact with the phase shift film 2 needs to have anextinction coefficient k higher than the upper layer 22 of the phaseshift film 2. The extinction coefficient k of the layer of the lightshielding film 3 in contact with the phase shift film 2 is preferably1.00 or more, more preferably 1.10 or more, and even more preferably1.20 or more. The above optical properties in the lower layer 21 andupper layer 22 of the phase shift film 2 and the layer of the lightshielding film 3 in contact with the phase shift film 2 can achieve theback-surface reflectance of 30% or more to the ArF exposure light. Thismakes it possible to suppress the photoexcitation of silicon atoms inthe phase shift film 2 and chromium atoms in the light shielding film 3.

If the light shielding film 3 is a laminated structure comprised of twoor more layers, various materials are applicable to layers of the lightshielding film 3 other than the layer in contact with the phase shiftfilm 2 (the lowermost layer). The material containing chromium describedabove is applicable to the layers of the light shielding film 3 otherthan the lowermost layer. The layers of the light shielding film 3 otherthan the lowermost layer may also be formed from a material containingtransition metal and silicon. This is because the material containingtransition metal and silicon has high light shielding performance, whichenables reduction of thickness of the light shielding film 3. Thetransition metal to be contained in the layers of the light shieldingfilm 3 other than the lowermost layer includes any one metal amongmolybdenum (Mo), tantalum (Ta), tungsten (W), titanium (Ti), hafnium(Hf), nickel (Ni), vanadium (V), zirconium (Zr), ruthenium (Ru), rhodium(Rh), zinc (Zn), niobium (Nb), palladium (Pd), etc., or an alloy ofthese metals. Metallic elements other than the transition metal elementsto be contained in the layers of the light shielding film 3 other thanthe lowermost layer include aluminum (Al), indium (In), tin (Sn),gallium (Ga), etc.

In the mask blank 100, a preferable structure is that a hard mask film 4formed from a material having etching selectivity to an etching gas usedin etching the light shielding film 3 is further laminated on the lightshielding film 3. Since the hard mask film 4 is not basically subject tothe limitation of optical density, the thickness of the hard mask film 4can be reduced significantly compared to the thickness of the lightshielding film 3. Since the thickness of a resist film of an organicmaterial is sufficient as long as the resist film functions as anetching mask until dry etching for forming a pattern in the hard maskfilm 4 is completed, the thickness can be reduced significantly comparedto conventional resist films. Reduction of thickness of a resist film iseffective for enhancing resist resolution and preventing collapse ofpattern, which is extremely important in addressing requirements forminiaturization.

In the case where the entire light shielding film 3 is formed from thematerial containing chromium, the hard mask film 4 is preferably formedfrom a material containing silicon. Since the hard mask film 4 in thiscase tends to have low adhesiveness with the resist film of an organicmaterial, it is preferable to treat the surface of the hard mask film 4with hexamethyldisilazane (HMDS) to enhance surface adhesiveness. Thehard mask film 4 in this case is more preferably formed from, forexample, SiO₂, SiN, or SiON.

Further, in the case where the light shielding film 3 is formed from thematerial containing chromium, a material containing tantalum is alsoapplicable as the material of the hard mask film 4, in addition to theabove. The material containing tantalum in this case includes, inaddition to tantalum metal, a material containing tantalum and one ormore elements selected from nitrogen, oxygen, boron, and carbon, such asTa, TaN, TaO, TaON, TaBN, TaBO, TaBON, TaCN, TaCO, TaCON, TaBCN, andTaBOCN. Further, in the case where the layers of the light shieldingfilm 3 other than the lowermost layer are formed from the materialcontaining silicon, the hard mask film 4 is preferably formed from thematerial containing chromium given above.

In the mask blank 100, a resist film of an organic material ispreferably formed in contact with a surface of the hard mask film 4 at athickness of 100 nm or less. In the case of a fine pattern to meet DRAMhp32 nm generation, a sub-resolution assist feature (SRAF) with 40 nmline width may be provided on a transfer pattern (phase shift pattern)to be formed in the hard mask film 4. However, even in this case, across-sectional aspect ratio of resist pattern can be as low as 1:2.5,and thus, the collapse and falling off of the resist pattern can beprevented in rinsing and developing the resist film. The resist filmmore preferably has a thickness of 80 nm or less.

FIGS. 2(a) to 2(g) show a phase shift mask 200 according to anembodiment of the present invention manufactured from the mask blank 100of the above embodiment, and its manufacturing process. As shown in FIG.2(g), the phase shift mask 200 features a phase shift pattern 2 a as atransfer pattern which is formed in the phase shift film 2 of the maskblank 100, and a light shielding pattern 3 b formed in the lightshielding film 3. If the hard mask film 4 is provided in the mask blank100, the hard mask film 4 is removed during manufacture of the phaseshift mask 200.

The method for manufacturing the phase shift mask 200 according to theembodiment of the present invention uses the mask blank 100 mentionedabove, and it features the steps of forming a transfer pattern in thelight shielding film 3 by dry etching; forming the transfer pattern inthe phase shift film 2 by dry etching using as a mask the lightshielding film 3 having the transfer pattern; and forming a lightshielding pattern 3 b in the light shielding film 3 by dry etching usingas a mask a second resist pattern 6 b that is a resist film having thelight shielding pattern. The method for manufacturing the phase shiftmask 200 according to the present invention is explained below inaccordance with the manufacturing process shown in FIGS. 2(a) to 2(g).Explained herein is the method for manufacturing the phase shift mask200 using the mask blank 100 having the hard mask film 4 laminated onthe light shielding film 3. In this method described here, the materialcontaining chromium is applied to all the layers of the light shieldingfilm 3 including the layer in contact with the phase shift film 2, andthe material containing silicon is applied to the hard mask film 4.

First, a resist film was formed in contact with the hard mask film 4 ofthe mask blank 100 by a spin coating method. Next, a first pattern,which was a transfer pattern (phase shift pattern) to be formed in thephase shift film 2, was exposed and drawn with electron beams on theresist film, and a predetermined treatment such as developing wasconducted, thereby forming a first resist pattern 5 a having the phaseshift pattern (see FIG. 2(a)). Subsequently, dry etching with afluorine-based gas was conducted using the first resist pattern 5 a as amask, and the first pattern (hard mask pattern 4 a) was formed in thehard mask film 4 (see FIG. 2(b)).

Next, after removing the first resist pattern 5 a, dry etching with amixed gas of a chlorine-based gas and an oxygen gas was conducted usingthe hard mask pattern 4 a as a mask, and the first pattern (lightshielding pattern 3 a) was formed in the light shielding film 3 (seeFIG. 2(c)). Subsequently, dry etching with the fluorine-based gas wasconducted using the light shielding pattern 3 a as a mask, and then thefirst pattern (phase shift pattern 2 a) was formed in the phase shiftfilm 2, and at the same time the hard mask pattern 4 a was removed (seeFIG. 2(d)).

Next, a resist film was formed on the mask blank 100 by the spin coatingmethod. Then, a second pattern, which was a pattern (light shieldingpattern) to be formed in the light shielding film 3, was exposed anddrawn with electron beams on the resist film, and a predeterminedtreatment such as developing was conducted, thereby forming a secondresist pattern 6 b having the light shielding pattern (see FIG. 2(e)).Subsequently, dry etching with the mixed gas of the chlorine-based gasand oxygen gas was conducted using the second resist pattern 6 b as amask, and the second pattern (light shielding pattern 3 b) was formed inthe light shielding film 3 (see FIG. 2(f)). Further, the second resistpattern 6 b was removed, a predetermined treatment such as cleaning wascarried out, and the phase shift mask 200 was obtained (FIG. 2(g)).

There is no particular limitation for the chlorine-based gas used forthe dry etching described above, as long as Cl is contained. Such achlorine-based gas includes, for example, Cl₂, SiCl₂, CHCl₃, CH₂Cl₂,CCl₄, and BCl₃. Further, there is no particular limitation for thefluorine-based gas used for the dry etching described above, as long asF is contained. Such a fluorine-based gas includes, for example, CHF₃,CF₄, C₂F₆, C₄F₈, and SF₆. Particularly, the fluorine-based gas free of Ccan further reduce damage on a glass substrate since it has a relativelylow etching rate to the glass substrate.

The phase shift mask 200 according to the present invention ismanufactured using the mask blank 100 described above. Thus, in thephase shift film 2 having the transfer pattern formed therein (phaseshift pattern 2 a), a transmittance to the ArF exposure light is withinthe range of not less than 2% and not more than 30%, and a phasedifference between the exposure light transmitted through the phaseshift pattern 2 a and the exposure light transmitted through the air forthe same distance as a thickness of the phase shift pattern 2 a iswithin the range of not less than 150 degrees and not more than 200degrees (more preferably not less than 150 degrees and not more than 180degrees). The phase shift mask 200 has a back-surface reflectance of 30%or more at a region on the transparent substrate 1 in the phase shiftpattern 2 a on which the light shielding pattern 3 b is laminated. Thismakes it possible to suppress the photoexcitation of silicon atoms inthe phase shift pattern 2 a and chromium atoms in the light shieldingpattern 3 b. This also makes it possible to suppress chromium migration,which is a phenomenon that the chromium atoms in the light shieldingpattern 3 b move into the phase shift pattern 2 a.

The phase shift mask 200 preferably has a back-surface reflectance of45% or less at a region on the transparent substrate 1 in the phaseshift pattern 2 a on which the light shielding pattern 3 b is laminated.This is for the purpose of preventing a large influence on an exposuretransfer image due to reflected light on the back-surface side of thephase shift pattern 2 a upon the exposure transfer to a transfer targetobject (such as a resist film on a semiconductor wafer) using the phaseshift mask 200.

The method for manufacturing a semiconductor device according to thepresent invention features the exposure transfer of a transfer patternto a resist film on a semiconductor substrate using the phase shift mask200 described above. In the phase shift pattern 2 a of the phase shiftmask 200, an influence of chromium migration can be considerablysuppressed. Thus, even if the phase shift mask 200 is set on an exposureapparatus and the step of irradiating ArF exposure light from thetransparent substrate 1 side of the phase shift mask 200 andexposure-transferring to a transfer target object (such as a resist filmon a semiconductor wafer) is carried out continuously, a desired patterncan be transferred continuously to respective transfer target objectswith high precision.

EXAMPLES

The embodiments of the present invention are described more specificallybelow along with examples.

Example 1

[Manufacture of Mask Blank]

A transparent substrate 1 formed from synthetic quartz glass, which hada main surface dimension of about 152 mm×about 152 mm and a thickness ofabout 6.35 mm, was prepared. End faces and main surfaces of thetransparent substrate 1 had been polished to have predetermined surfaceroughness, and then subjected to predetermined cleaning and dryingtreatments. The optical properties of the transparent substrate 1 weremeasured, and the refractive index n was 1.56 and extinction coefficientk was 0.00.

Next, the transparent substrate 1 was placed in a single-wafer DCsputtering apparatus, and by reactive sputtering (DC sputtering) using amixed target of molybdenum (Mo) and silicon (Si) (Mo:Si=11 atomic %:89atomic %) with a mixed gas of argon (Ar) and helium (He) as a sputteringgas, a lower layer 21 of the phase shift film 2 formed from molybdenumand silicon (MoSi film) was formed on the transparent substrate 1 at athickness of 7 nm.

Then, the transparent substrate 1 having the lower layer 21 formedthereon was placed in the single-wafer DC sputtering apparatus, and byreactive sputtering (DC sputtering) using a mixed target of molybdenum(Mo) and silicon (Si) (Mo:Si=4 atomic %: 96 atomic %) with a mixed gasof argon (Ar), nitrogen (N₂), oxygen (O₂), and helium (He) as asputtering gas, an upper layer 22 of the phase shift film 2 formed frommolybdenum, silicon, nitrogen, and oxygen (MoSiON film) was formed onthe lower layer 21 at a thickness of 72 nm. By the above procedure, thephase shift film 2 including the laminated lower and upper layers 21 and22 was formed in contact with a surface of the transparent substrate 1at a thickness of 79 nm.

Next, to reduce film stress of the phase shift film 2 and to form anoxidized layer on the surface layer, the transparent substrate 1 havingthe phase shift film 2 formed thereon was subjected to a heat treatment.In particular, a heating furnace (electric furnace) was used to conductthe heat treatment at a heating temperature of 450° C. in the air forone hour. Another transparent substrate 1, which had a phase shift film2 including laminated lower and upper layers 21 and 22 on its mainsurface formed under the same conditions, was prepared and subjected tothe heat treatment. The transmittance and phase difference of the phaseshift film 2 to the light at a wavelength of 193 nm were measured usinga phase shift amount measurement device (MPM193 manufactured by LasertecCorporation). As a result, the transmittance was 6.0%, and the phasedifference was 170.0 degrees. Further, the phase shift film 2 wasanalyzed by the scanning electron microscope (STEM) and energydispersive X-ray spectroscopy (EDX), and formation of the oxidized layerhaving a thickness of about 1.7 nm measured from the surface of theupper layer 22 of the phase shift film 2 was confirmed. Moreover, theoptical properties were measured for each of the lower layer 21 and theupper layer 22 of the phase shift film 2. As a result, the lower layer21 had the refractive index n of 1.15 and the extinction coefficient kof 2.90, and the upper layer 22 had the refractive index n of 2.38 andthe extinction coefficient k of 0.31.

Next, the transparent substrate 1 having the phase shift film 2 formedthereon was placed in the single-wafer DC sputtering apparatus, and byreactive sputtering (DC sputtering) using a chromium (Cr) target with amixed gas of argon (Ar), carbon dioxide (CO₂), nitrogen (N₂), and helium(He) as a sputtering gas, a light shielding film 3 formed from CrOCN(CrOCN film: Cr:O:C:N=55 atomic %:22 atomic %:12 atomic %:11 atomic %)was formed on the phase shift film 2 at a thickness of 46 nm. In themask blank 100, the back-surface reflectance (reflectance on thetransparent substrate 1 side) to the light at a wavelength of 193 nmwhile the phase shift film 2 and the light shielding film 3 werelaminated on the transparent substrate 1 was 40.9%. The optical density(OD) of the laminated structure of the phase shift film 2 and the lightshielding film 3 to the light at a wavelength of 193 nm as measured was3.0 or more. Further, another transparent substrate 1 was prepared, onlya light shielding film 3 was formed under the same film-formingconditions, and the optical properties of the light shielding film 3were measured. As a result, the refractive index n was 1.95, and theextinction coefficient k was 1.53. The composition of the lightshielding film 3 is the result obtained from measurement by X-rayphotoelectron spectroscopy (XPS). The same applies to other filmshereafter.

Next, the transparent substrate 1 with the phase shift film 2 and thelight shielding film 3 laminated thereon was placed in a single-wafer RFsputtering apparatus, and by RF sputtering using a silicon dioxide(SiO₂) target with an argon (Ar) gas as a sputtering gas, a hard maskfilm 4 formed from silicon and oxygen was formed on the light shieldingfilm 3 at a thickness of 5 nm. Through the above procedure, the maskblank 100 having a structure in which the phase shift film 2 of atwo-layer structure, the light shielding film 3, and the hard mask film4 were laminated on the transparent substrate 1 was manufactured.

[Manufacture of Phase Shift Mask]

Then, a phase shift mask 200 of Example 1 was manufactured through thefollowing procedure using the mask blank 100 of Example 1. First, asurface of the hard mask film 4 was subjected to the HMDS treatment.Subsequently, a resist film made of a chemically amplified resist forelectron beam writing was formed in contact with a surface of the hardmask film 4 by the spin coating method at a thickness of 80 nm. Next, afirst pattern, which was a phase shift pattern to be formed in the phaseshift film 2, was drawn on the resist film with electron beams,predetermined cleaning and developing treatments were conducted, and afirst resist pattern 5 a having the first pattern was formed (see FIG.2(a)).

Next, dry etching with a CF₄ gas was conducted using the first resistpattern 5 a as a mask, and the first pattern (hard mask pattern 4 a) wasformed in the hard mask film 4 (see FIG. 2(b)).

Then, the first resist pattern 5 a was removed. Subsequently, dryetching with a mixed gas of chlorine and oxygen (gas flow ratio ofCl₂:O₂=4:1) was conducted using the hard mask pattern 4 a as a mask, andthe first pattern (light shielding pattern 3 a) was formed in the lightshielding film 3 (see FIG. 2(c)). Next, dry etching with thefluorine-based gas (SF₆+He) was conducted using the light shieldingpattern 3 a as a mask, and then the first pattern (phase shift pattern 2a) was formed in the phase shift film 2, and at the same time the hardmask pattern 4 a was removed (see FIG. 2(d)).

Next, a resist film made of a chemically amplified resist for electronbeam writing was formed on the light shielding pattern 3 a by the spincoating method at a thickness of 150 nm. Then, a second pattern, whichwas a pattern (light shielding band pattern) to be formed in the lightshielding film, was exposed and drawn on the resist film, apredetermined treatment such as developing was further conducted, and asecond resist pattern 6 b having the light shielding pattern was formed(see FIG. 2(e)). Subsequently, dry etching with the mixed gas ofchlorine and oxygen (gas flow ratio of Cl₂:O₂=4:1) was conducted usingthe second resist pattern 6 b as a mask, and the second pattern wasformed in the light shielding film 3 (see FIG. 2(f)). Further, thesecond resist pattern 6 b was removed, a predetermined treatment such ascleaning was carried out, and the phase shift mask 200 was obtained (seeFIG. 2(g)).

A region of the phase shift pattern 2 a on which the light shieldingpattern 3 b was laminated in the manufactured phase shift mask 200 ofExample 1 was subjected to an irradiation treatment in which ArF excimerlaser light was intermittently irradiated until an accumulatedirradiation amount reached 40 kJ/cm². Using AIMS193 (manufactured byCarl Zeiss), a simulation of an exposure transfer image upon theexposure transfer to a resist film on a semiconductor device with theexposure light at a wavelength of 193 nm was performed on the phaseshift mask 200 after the irradiation treatment. As a result ofinspection of the exposure transfer image obtained by the simulation, itwas found that the design specification was fully satisfied. It can beconsidered from this result that the exposure transfer can be made onthe resist film on the semiconductor device with high precision, even ifthe phase shift mask 200 manufactured from the mask blank 100 of Example1 was set on an exposure apparatus and subjected to exposure transfer byexposure light of an ArF excimer laser until the accumulated irradiationamount reached 40 kJ/cm².

Further, measurement by secondary ion mass spectrometry (SIMS) was madeon the irradiated region of the phase shift pattern 2 a of the phaseshift mask 200 of Example 1. As a result, it was found that the phaseshift pattern 2 a contained a slight amount of chromium. It can beconsidered from this result that the phase shift mask 200 manufacturedfrom the mask blank 100 of Example 1 can sufficiently suppress aphenomenon of movement of chromium in the light shielding pattern 3 binto the phase shift pattern 2 a (chromium migration) even if exposurelight of the ArF excimer laser is irradiated on the phase shift pattern2 a on which the light shielding pattern 3 b is laminated.

Example 2

[Manufacture of Mask Blank]

The mask blank 100 of Example 2 was manufactured through a proceduresimilar to Example 1, except for the phase shift film 2. The changesmade in the phase shift film 2 of Example 2 are the respective materialsforming the lower layer 21 and the upper layer 22, and their thickness.Specifically, the transparent substrate 1 was placed in a single-waferDC sputtering apparatus, and by reactive sputtering (DC sputtering)using a mixed target of molybdenum (Mo) and silicon (Si) (Mo:Si=11atomic %:89 atomic %) with a mixed gas of argon (Ar), nitrogen (N₂), andhelium (He) as a sputtering gas, a lower layer 21 of the phase shiftfilm 2 formed from molybdenum, silicon, and nitrogen (MoSiN film) wasformed on the transparent substrate 1 at a thickness of 7 nm.

Next, the transparent substrate 1 having the lower layer 21 formedthereon was placed in the single-wafer DC sputtering apparatus, and byreactive sputtering (DC sputtering) using a mixed target of molybdenum(Mo) and silicon (Si) (Mo:Si=8 atomic %:92 atomic %) with a mixed gas ofargon (Ar), nitrogen (N₂), oxygen (O₂), and helium (He) as a sputteringgas, an upper layer 22 of the phase shift film 2 formed from molybdenum,silicon, nitrogen, and oxygen (MoSiON film) was formed on the lowerlayer 21 at a thickness of 88 nm. By the above procedure, the phaseshift film 2 including the laminated lower and upper layers 21 and 22was formed in contact with a surface of the transparent substrate 1 at athickness of 95 nm.

Further, the phase shift film 2 of Example 2 was also subjected to theheat treatment under the treatment conditions similar to Example 1.Another transparent substrate 1, which had the phase shift film 2 ofExample 2 on its main surface formed under the same conditions, wasprepared and subjected to the heat treatment. The transmittance andphase difference of the phase shift film 2 to the light at a wavelengthof 193 nm were measured using a phase shift amount measurement device(MPM193 manufactured by Lasertec Corporation). As a result, thetransmittance was 6.0%, and the phase difference was 170.4 degrees.Further, the phase shift film 2 was analyzed by STEM and EDX, andformation of an oxidized layer having a thickness of about 1.6 nmmeasured from the surface of the upper layer 22 of the phase shift film2 was confirmed. Moreover, the optical properties were measured for eachof the lower layer 21 and the upper layer 22 of the phase shift film 2.As a result, the lower layer 21 had the refractive index n of 1.34 andthe extinction coefficient k of 2.79, and the upper layer 22 had therefractive index n of 2.13 and the extinction coefficient k of 0.28.

By the above procedure, the mask blank 100 of Example 2 wasmanufactured, the mask blank 100 having a structure in which the phaseshift film 2 including the lower layer 21 of MoSiN and the upper layer22 of MoSiON, the light shielding film 3 having a single-layer structureof CrOCN, and the hard mask film 4 were laminated on the transparentsubstrate 1. In the mask blank 100, the back-surface reflectance(reflectance on the transparent substrate 1 side) to the light at awavelength of 193 nm while the phase shift film 2 and the lightshielding film 3 were laminated on the transparent substrate 1 was36.5%. The optical density (OD) of the laminated structure of the phaseshift film 2 and the light shielding film 3 to the light at a wavelengthof 193 nm as measured was 3.0 or more.

[Manufacture of Phase Shift Mask]

Next, the phase shift mask 200 of Example 2 was manufactured through aprocedure similar to Example 1 using the mask blank 100 of Example 2.

A region of the phase shift pattern 2 a on which the light shieldingpattern 3 b was laminated in the manufactured phase shift mask 200 ofExample 2 was subjected to an irradiation treatment in which ArF excimerlaser light was intermittently irradiated until an accumulatedirradiation amount reached 40 kJ/cm². Using AIMS193 (manufactured byCarl Zeiss), a simulation of an exposure transfer image upon theexposure transfer to a resist film on a semiconductor device with theexposure light at a wavelength of 193 nm was performed on the phaseshift mask 200 after the irradiation treatment. As a result ofinspection of the exposure transfer image obtained by the simulation, itwas found that the design specification was fully satisfied. It can beconsidered from this result that the exposure transfer can be made onthe resist film on the semiconductor device with high precision, even ifthe phase shift mask 200 manufactured from the mask blank 100 of Example2 was set on an exposure apparatus and subjected to exposure transfer byexposure light of an ArF excimer laser until the accumulated irradiationamount reached 40 kJ/cm².

Further, measurement by secondary ion mass spectrometry (SIMS) was madeon the irradiated region of the phase shift pattern 2 a of the half tonephase shift mask 200 of Example 2. As a result, it was found that thephase shift pattern 2 a contained a slight amount of chromium. It can beconsidered from this result that the phase shift mask 200 manufacturedfrom the mask blank 100 of Example 2 can sufficiently suppress aphenomenon of movement of chromium in the light shielding pattern 3 binto the phase shift pattern 2 a (chromium migration) even if exposurelight of the ArF excimer laser is irradiated on the phase shift pattern2 a on which the light shielding pattern 3 b is laminated.

Example 3

[Manufacture of Mask Blank]

The mask blank 100 of Example 3 was manufactured through a proceduresimilar to Example 1, except for the light shielding film 3. The lightshielding film 3 of Example 3 has a structure in which a lowermost layer(layer in contact with the phase shift film 2) and an upper layer arelaminated from the phase shift film 2 side. Specifically, thetransparent substrate 1 having the phase shift film 2 formed thereon wasplaced in a single-wafer DC sputtering apparatus, and by reactivesputtering (DC sputtering) using a chromium (Cr) target with a mixed gasof argon (Ar), nitrogen (N₂), carbon dioxide (CO₂), and helium (He) as asputtering gas, the lowermost layer of the light shielding film 3 formedfrom chromium, oxygen, nitrogen, and carbon (CrOCN film: Cr:O:C:N=49atomic %:24 atomic %:13 atomic %:14 atomic %) was formed on the phaseshift film 2 at a thickness of 47 nm. Subsequently, by reactivesputtering (DC sputtering) also using a chromium (Cr) target with amixed gas of argon (Ar) and nitrogen (N₂) as a sputtering gas, the upperlayer of the light shielding film 3 formed from chromium and nitrogen(CrN film: Cr:N=76 atomic %:24 atomic %) was formed on the lowermostlayer at a thickness of 5 nm.

By the above procedure, the mask blank 100 of Example 3 wasmanufactured, the mask blank 100 having a structure in which the phaseshift film 2 including the lower layer 21 of MoSi and the upper layer 22of MoSiON, the light shielding film 3 including the lowermost layer ofCrOCN and the upper layer of CrN, and the hard mask film 4 werelaminated on the transparent substrate. In the mask blank 100, theback-surface reflectance (reflectance on the transparent substrate 1side) to the light at a wavelength of 193 nm while the phase shift film2 and the light shielding film 3 were laminated on the transparentsubstrate 1 was 40.9%. The optical density (OD) of the laminatedstructure of the phase shift film 2 and the light shielding film 3 tothe light at a wavelength of 193 nm as measured was 3.0 or more.Further, another transparent substrate 1 was prepared, only a lightshielding film 3 was formed under the same film-forming conditions, andthe optical properties of the light shielding film 3 were measured. As aresult, the lowermost layer of the light shielding film 3 had arefractive index n of 1.78 and an extinction coefficient k of 1.20. Theupper layer of the light shielding film 3 had a refractive index n of1.55 and an extinction coefficient k of 1.68.

[Manufacture of Phase Shift Mask]

Next, the phase shift mask 200 of Example 3 was manufactured through aprocedure similar to Example 1 using the mask blank 100 of Example 3.

A region of the phase shift pattern 2 a on which the light shieldingpattern 3 b was laminated in the manufactured phase shift mask 200 ofExample 3 was subjected to an irradiation treatment in which ArF excimerlaser light was intermittently irradiated until an accumulatedirradiation amount reached 40 kJ/cm². Using AIMS193 (manufactured byCarl Zeiss), a simulation of an exposure transfer image upon theexposure transfer to a resist film on a semiconductor device with theexposure light at a wavelength of 193 nm was performed on the phaseshift mask 200 after the irradiation treatment. As a result ofinspection of the exposure transfer image obtained by the simulation, itwas found that the design specification was fully satisfied. It can beconsidered from this result that the exposure transfer can be made onthe resist film on the semiconductor device with high precision, even ifthe phase shift mask 200 manufactured from the mask blank 100 of Example3 was set on an exposure apparatus and subjected to exposure transfer byexposure light of an ArF excimer laser until the accumulated irradiationamount reached 40 kJ/cm².

Further, measurement by secondary ion mass spectrometry (SIMS) was madeon the irradiated region of the phase shift pattern 2 a of the half tonephase shift mask 200 of Example 3. As a result, it was found that thephase shift pattern 2 a contained a slight amount of chromium. It can beconsidered from this result that the phase shift mask 200 manufacturedfrom the mask blank 100 of Example 3 can sufficiently suppress aphenomenon of movement of chromium in the light shielding pattern 3 binto the phase shift pattern 2 a (chromium migration) even if exposurelight of the ArF excimer laser is irradiated on the phase shift pattern2 a on which the light shielding pattern 3 b is laminated.

Example 4

[Manufacture of Mask Blank]

The mask blank 100 of Example 4 was manufactured through a proceduresimilar to Example 2, except for the light shielding film 3. The lightshielding film 3 of Example 4 was the same as the light shielding film 3of Example 3. By the above procedure, the mask blank 100 of Example 4was manufactured, the mask blank 100 having a structure in which thephase shift film 2 including the lower layer 21 of MoSiN and the upperlayer 22 of MoSiON, the light shielding film 3 including the lowermostlayer of CrOCN and the upper layer of CrN, and the hard mask film 4 werelaminated on the transparent substrate. In the mask blank 100, theback-surface reflectance (reflectance on the transparent substrate 1side) to the light at a wavelength of 193 nm while the phase shift film2 and the light shielding film 3 were laminated on the transparentsubstrate 1 was 34.9%. The optical density (OD) of the laminatedstructure of the phase shift film 2 and the light shielding film 3 tothe light at a wavelength of 193 nm as measured was 3.0 or more.

[Manufacture of Phase Shift Mask]

Next, the phase shift mask 200 of Example 4 was manufactured through aprocedure similar to Example 1 using the mask blank 100 of Example 4.

A region of the phase shift pattern 2 a on which the light shieldingpattern 3 b was laminated in the manufactured phase shift mask 200 ofExample 4 was subjected to an irradiation treatment in which ArF excimerlaser light was intermittently irradiated until an accumulatedirradiation amount reached 40 kJ/cm². Using AIMS193 (manufactured byCarl Zeiss), a simulation of an exposure transfer image upon theexposure transfer to a resist film on a semiconductor device with theexposure light at a wavelength of 193 nm was performed on the phaseshift mask 200 after the irradiation treatment. As a result ofinspection of the exposure transfer image obtained by the simulation, itwas found that the design specification was fully satisfied. It can beconsidered from this result that the exposure transfer can be made onthe resist film on the semiconductor device with high precision, even ifthe phase shift mask 200 manufactured from the mask blank 100 of Example4 was set on an exposure apparatus and subjected to exposure transfer byexposure light of an ArF excimer laser until the accumulated irradiationamount reached 40 kJ/cm².

Further, measurement by secondary ion mass spectrometry (SIMS) was madeon the irradiated region of the phase shift pattern 2 a of the half tonephase shift mask 200 of Example 4. As a result, it was found that thephase shift pattern 2 a contained a slight amount of chromium. It can beconsidered from this result that the phase shift mask 200 manufacturedfrom the mask blank 100 of Example 4 can sufficiently suppress aphenomenon of movement of chromium in the light shielding pattern 3 binto the phase shift pattern 2 a (chromium migration) even if exposurelight of the ArF excimer laser is irradiated on the phase shift pattern2 a on which the light shielding pattern 3 b is laminated.

Example 5

[Manufacture of Mask Blank]

The mask blank 100 of Example 5 was manufactured through a proceduresimilar to Example 1, except for the phase shift film 2. The changesmade in the phase shift film 2 of Example 5 are the respective materialsforming the lower layer 21 and the upper layer 22, and their thickness.Specifically, the transparent substrate 1 was placed in a single-waferRF sputtering apparatus, and by RF sputtering using a silicon (Si)target with an argon (Ar) gas as a sputtering gas, the lower layer 21 ofthe phase shift film 2 formed from silicon (Si film) was formed incontact with a surface of the transparent substrate 1 at a thickness of8 nm. Subsequently, by reactive sputtering (RF sputtering) using asilicon (Si) target with a mixed gas of argon (Ar) and nitrogen (N₂) asa sputtering gas, the upper layer 22 of the phase shift film 2 formedfrom silicon and nitrogen (SiN film: Si:N=43 atomic %:57 atomic %) wasformed on the lower layer 21 at a thickness of 63 nm. By the aboveprocedure, the phase shift film 2 including the laminated lower andupper layers 21 and 22 was formed in contact with the surface of thetransparent substrate 1 at a thickness of 71 nm.

Further, to reduce film stress of the phase shift film 2 and to form anoxidized layer on the surface layer portion, the transparent substrate 1having the phase shift film 2 formed thereon was subjected to a heattreatment. The transmittance and phase difference of the phase shiftfilm 2 to the light at a wavelength of 193 nm were measured using aphase shift amount measurement device (MPM193 manufactured by LasertecCorporation). As a result, the transmittance was 6.1%, and the phasedifference was 177.0 degrees. Further, the phase shift film 2 wasanalyzed by STEM and EDX, and formation of the oxidized layer in thesurface layer portion at a thickness of about 2 nm from the surface ofthe upper layer 22 was confirmed.

By the above procedure, the mask blank 100 of Example 5 wasmanufactured, the mask blank 100 having a structure in which the phaseshift film 2 including the lower layer 21 of Si and the upper layer 22of SiN, the light shielding film 3 having a single-layer structure ofCrOCN, and the hard mask film 4 were laminated on the transparentsubstrate 1. In the mask blank 100, the back-surface reflectance(reflectance on the transparent substrate 1 side) to the light at awavelength of 193 nm while the phase shift film 2 and the lightshielding film 3 were laminated on the transparent substrate 1 was42.7%. The optical density (OD) of the laminated structure of the phaseshift film 2 and the light shielding film 3 to the light at a wavelengthof 193 nm as measured was 3.0 or more. Further, another transparentsubstrate 1 was prepared, only a phase shift film 2 was formed under thesame film-forming conditions, and the optical properties of the phaseshift film 2 were measured. As a result, the lower layer 21 had arefractive index n of 1.06 and an extinction coefficient k of 2.72, andthe upper layer 22 had a refractive index n of 2.63 and an extinctioncoefficient k of 0.37.

[Manufacture of Phase Shift Mask]

Next, the phase shift mask 200 of Example 5 was manufactured through aprocedure similar to Example 1 using the mask blank 100 of Example 5.

A region of the phase shift pattern 2 a on which the light shieldingpattern 3 b was laminated in the manufactured phase shift mask 200 ofExample 5 was subjected to an irradiation treatment in which ArF excimerlaser light was intermittently irradiated until an accumulatedirradiation amount reached 40 kJ/cm². Using AIMS193 (manufactured byCarl Zeiss), a simulation of an exposure transfer image upon theexposure transfer to a resist film on a semiconductor device with theexposure light at a wavelength of 193 nm was performed on the phaseshift mask 200 after the irradiation treatment. As a result ofinspection of the exposure transfer image obtained by the simulation, itwas found that the design specification was fully satisfied. It can beconsidered from this result that the exposure transfer can be made onthe resist film on the semiconductor device with high precision, even ifthe phase shift mask 200 manufactured from the mask blank 100 of Example5 was set on an exposure apparatus and subjected to exposure transfer byexposure light of an ArF excimer laser until the accumulated irradiationamount reached 40 kJ/cm².

Further, measurement by secondary ion mass spectrometry (SIMS) was madeon the irradiated region of the phase shift pattern 2 a of the half tonephase shift mask 200 of Example 5. As a result, it was found that thephase shift pattern 2 a contained a slight amount of chromium. It can beconsidered from this result that the phase shift mask 200 manufacturedfrom the mask blank 100 of Example 5 can sufficiently suppress aphenomenon of movement of chromium in the light shielding pattern 3 binto the phase shift pattern 2 a (chromium migration) even if exposurelight of the ArF excimer laser is irradiated on the phase shift pattern2 a on which the light shielding pattern 3 b is laminated.

Comparative Example 1

[Manufacture of Mask Blank]

The mask blank of Comparative Example 1 was manufactured through aprocedure similar to Example 1, except for the phase shift film 2. Afilm of a single layer structure made of molybdenum, silicon, andnitrogen was used as the phase shift film of Comparative Example 1.Specifically, the transparent substrate 1 was placed in a single-waferDC sputtering apparatus, and by reactive sputtering (DC sputtering)using a mixed sintered target of molybdenum (Mo) and silicon (Si)(Mo:Si=11 atomic %:89 atomic %) with a mixed gas of argon (Ar), nitrogen(N₂), and helium (He) as a sputtering gas, the phase shift film 2 formedfrom molybdenum, silicon, and nitrogen was formed at a thickness of 69nm.

Further, this phase shift film was also subjected to the heat treatmentunder the treatment conditions similar to Example 1. Another transparentsubstrate 1, which had the phase shift film of Comparative Example 1 onits main surface formed under the same conditions, was prepared andsubjected to the heat treatment. The transmittance and phase differenceof the phase shift film to the light at a wavelength of 193 nm weremeasured using a phase shift amount measurement device (MPM193manufactured by Lasertec Corporation). As a result, the transmittancewas 6.1%, and the phase difference was 177.0 degrees. Further, the phaseshift film was analyzed by STEM and EDX, and formation of an oxidizedlayer having a thickness of about 2 nm measured from the surface of thephase shift film was confirmed.

By the above procedure, the mask blank of Comparative Example 1 wasmanufactured, the mask blank having a structure in which the phase shiftfilm of MoSiN, a light shielding film having a single layer structure ofCrOCN, and a hard mask film were laminated on the transparent substrate1. In the mask blank, the back-surface reflectance (reflectance on thetransparent substrate 1 side) to the light at a wavelength of 193 nmwhile the phase shift film and the light shielding film were laminatedon the transparent substrate 1 was 11.0%. The optical density (OD) ofthe laminated structure of the phase shift film and the light shieldingfilm to the light at a wavelength of 193 nm as measured was 3.0 or more.Further, another transparent substrate was prepared, only a phase shiftfilm was formed under the same film-forming conditions, and the opticalproperties of the phase shift film were measured. As a result, therefractive index n was 2.39, and the extinction coefficient k was 0.57.

[Manufacture of Phase Shift Mask]

Next, the phase shift mask of Comparative Example 1 was manufacturedthrough a procedure similar to Example 1 using the mask blank ofComparative Example 1.

A region of the phase shift pattern on which the light shielding patternwas laminated in the manufactured phase shift mask of ComparativeExample 1 was subjected to an irradiation treatment in which ArF excimerlaser light was intermittently irradiated until an accumulatedirradiation amount reached 40 kJ/cm². Using AIMS193 (manufactured byCarl Zeiss), a simulation of an exposure transfer image upon theexposure transfer to a resist film on a semiconductor device with theexposure light at a wavelength of 193 nm was performed on the phaseshift mask after the irradiation treatment. As a result of inspection ofthe exposure transfer image obtained by the simulation, it was foundthat the design specification was not satisfied. It can be consideredfrom this result that a highly precise exposure transfer cannot be madeon the resist film on the semiconductor device when the phase shift maskmanufactured from the mask blank of Comparative Example 1 was set on anexposure apparatus and subjected to exposure transfer by exposure lightof an ArF excimer laser until the accumulated irradiation amount reached40 kJ/cm².

Further, the region of the phase shift pattern on which the lightshielding pattern was laminated in the phase shift mask of ComparativeExample 1 was subjected to an irradiation treatment in which ArF excimerlaser light was intermittently irradiated until an accumulatedirradiation amount reached 40 kJ/cm². Secondary ion mass spectrometry(SIMS) was conducted on the irradiated region of the phase shiftpattern. As a result, it was found that the chromium content in thephase shift pattern was significantly higher than the results inExamples. It can be considered from this result that the phase shiftmask manufactured from the mask blank of Comparative Example 1 cannotsuppress movement of chromium in the light shielding pattern into thephase shift pattern when exposure light of the ArF excimer laser isirradiated on the phase shift pattern on which the light shieldingpattern is laminated.

DESCRIPTION OF REFERENCE NUMERALS

-   1: transparent substrate-   2: phase shift film-   21: lower layer-   22: upper layer-   2 a: phase shift pattern-   3: light shielding film-   3 a, 3 b: light shielding pattern-   4: hard mask film-   4 a: hard mask pattern-   5 a: first resist pattern-   6 b: second resist pattern-   100: mask blank-   200: phase shift mask

What is claimed is:
 1. A mask blank having a structure in which a phaseshift film and a light shielding film are laminated in this order on atransparent substrate, wherein the phase shift film has a function totransmit exposure light of an ArF excimer laser at a transmittance ofnot less than 2% and not more than 30%, and a function to generate aphase difference of not less than 150 degrees and not more than 200degrees between the exposure light transmitted through the phase shiftfilm and the exposure light transmitted through air for the samedistance as a thickness of the phase shift film, wherein the phase shiftfilm is formed from a material containing silicon and not substantiallycontaining chromium, and includes a structure in which a lower layer andan upper layer are laminated from the transparent substrate side,wherein the lower layer has a refractive index n lower than thetransparent substrate at a wavelength of the exposure light, wherein theupper layer has a refractive index n higher than the transparentsubstrate at a wavelength of the exposure light, wherein the lower layerhas an extinction coefficient k higher than the upper layer at awavelength of the exposure light, wherein the light shielding filmincludes a layer in contact with the phase shift film, and wherein thelayer in contact with the phase shift film is formed from a materialcontaining chromium, has a refractive index n lower than the upper layerat a wavelength of the exposure light, and has an extinction coefficientk higher than the upper layer at a wavelength of the exposure light. 2.The mask blank according to claim 1, wherein the upper layer has athickness greater than the lower layer.
 3. The mask blank according toclaim 1, wherein the lower layer has a thickness of less than 10 nm. 4.The mask blank according to claim 1, wherein the refractive index n ofthe lower layer is 1.5 or less.
 5. The mask blank according to claim 1,wherein the refractive index n of the upper layer is greater than 2.0.6. The mask blank according to claim 1, wherein the refractive index nof the layer in contact with the phase shift film is 2.0 or less.
 7. Themask blank according to claim 1, wherein the extinction coefficient k ofthe lower layer is 2.0 or more.
 8. The mask blank according to claim 1,wherein an extinction coefficient k of the upper layer is 0.8 or less.9. The mask blank according to claim 1, wherein the extinctioncoefficient k of the layer in contact with the phase shift film is 1.0or more.
 10. The mask blank according to claim 1, wherein the lowerlayer is formed in contact with a surface of the transparent substrate.11. The mask blank according to claim 1, wherein the upper layer has inits surface layer a layer having an oxygen content higher than in theportion of the upper layer excluding the surface layer.
 12. The maskblank according to claim 1, wherein a back-surface reflectance to theexposure light entering from the transparent substrate side is 30% ormore.
 13. A phase shift mask having a structure in which a phase shiftfilm having a transfer pattern formed therein and a light shielding filmhaving a light shielding pattern formed therein are laminated in thisorder on a transparent substrate, wherein the phase shift film has afunction to transmit exposure light of an ArF excimer laser at atransmittance of not less than 2% and not more than 30%, and a functionto generate a phase difference of not less than 150 degrees and not morethan 200 degrees between the exposure light transmitted through thephase shift film and the exposure light transmitted through air for thesame distance as a thickness of the phase shift film, wherein the phaseshift film is formed from a material containing silicon and notsubstantially containing chromium, and includes a structure in which alower layer and an upper layer are laminated from the transparentsubstrate side, wherein the lower layer has a refractive index n lowerthan the transparent substrate at a wavelength of the exposure light,wherein the upper layer has a refractive index n higher than thetransparent substrate at a wavelength of the exposure light, wherein thelower layer has an extinction coefficient k higher than the upper layerat a wavelength of the exposure light, wherein the light shielding filmincludes a layer in contact with the phase shift film, and wherein thelayer in contact with the phase shift film is formed from a materialcontaining chromium, has a refractive index n lower than the upper layerat a wavelength of the exposure light, and has an extinction coefficientk higher than the upper layer at a wavelength of the exposure light. 14.The phase shift mask according to claim 13, wherein the upper layer hasa thickness greater than the lower layer.
 15. The phase shift maskaccording to claim 13, wherein the lower layer has a thickness of lessthan 10 nm.
 16. The phase shift mask according to claim 13, wherein therefractive index n of the lower layer is 1.5 or less.
 17. The phaseshift mask according to claim 13, wherein the refractive index n of theupper layer is greater than 2.0.
 18. The phase shift mask according toclaim 13, wherein the refractive index n of the layer in contact withthe phase shift film is 2.0 or less.
 19. The phase shift mask accordingto claim 13, wherein the extinction coefficient k of the lower layer is2.0 or more.
 20. The phase shift mask according to claim 13, wherein anextinction coefficient k of the upper layer is 0.8 or less.
 21. Thephase shift mask according to claim 13, wherein the extinctioncoefficient k of the layer in contact with the phase shift film is 1.0or more.
 22. The phase shift mask according to claim 13, wherein thelower layer is formed in contact with a surface of the transparentsubstrate.
 23. The phase shift mask according to claim 13, wherein theupper layer has in its surface layer a layer having an oxygen contenthigher than in the portion of the upper layer excluding the surfacelayer.
 24. The phase shift mask according to claim 13, wherein aback-surface reflectance to the exposure light entering from thetransparent substrate side is 30% or more.
 25. A method formanufacturing a semiconductor device comprising the step of using thephase shift mask according to claim 13 and exposure-transferring atransfer pattern to a resist film on a semiconductor substrate.